Image recording method, energy radiation curable ink and image recording apparatus

ABSTRACT

An image recording method, an image recording apparatus and energy radiation curable ink which can print high-quality images. The image recording method for ejecting and placing energy radiation curable ink which is cured when irradiated with energy radiation according to an ink-jet recording method, irradiating the energy radiation on a recording medium on which ink dots are formed, and printing an image, has: ejecting the energy radiation curable ink to the recording medium from a plurality of nozzles provided for an ink-jet head, moving the recording medium to the ink-jet head relatively, and forming the image; and controlling a range to which the energy radiation is irradiated, so as to correspond to a recording width of the ink-jet head.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to energy radiation curable inkhaving a property to be cured when irradiated with energy radiation suchas UV radiation, infrared radiation or the like, and an image recordingmethod and an image recording apparatus for using the energy radiationcurable ink and forming an image according to an ink-jet system.

[0003] 2. Description of Related Art

[0004] An ink-jet recording method is an image printing methodapplicable to an on-demand print with a view to printing a small numberof copies. In recent years, attention is paid to the ink-jet recordingmethod, because specific papers are not required for the ink-jetrecording method. An energy radiation curable ink jet system of theink-jet recording method is a printing system for placing energyradiation curable ink having a proper to be cured when irradiated withenergy radiation such as UV radiation or the like, on a recordingmedium, irradiating the energy radiation to the recording medium, andthereby curing the energy radiation curable ink.

[0005] A UV ink jet system as a kind of the energy radiation curable inkjet system is a printing system using UV ink having a property to becured when irradiated with UV radiation as a kind of the energyradiation, as the energy radiation curable ink. According to the UV inkjet system, it is possible to print high-quality images by irradiatingUV radiation and controlling a diameter of a dot placed.

[0006] In order to control the diameter of the dot placed, it isnecessary to cure the UV ink immediately after placed on the recordingmedium. In order to cure the UV ink rapidly as described above, forexample, there is a method that provides a UV light source such as amercury lamp, a metal halide lamp, or the like, for a carriage holdingan ink-jet head for ejecting ink so as to be movable, as disclosed inJapanese Patent Application Publication (Unexamined) No. Tokukai-sho60-132767, and U.S. Pat. No. 61,459,797. However, according to themethod, there is a problem that the weight of the carriage becomesheavy, the acceleration of the carriage is reduced, the efficiency ofthe image printing operation is lowered, or the whole ink-jet printer isbulky.

[0007] Further, a method has been known, the method for irradiating UVradiation from the carriage by using an optical fiber, or introducing UVradiation which is parallel rays with a mirror, as disclosed in JapanesePatent Application Publication (Unexamined) No. Tokukai-sho 60-132767,and U.S. Pat. No. 61,459,797. However, because the optical fiber is notbent very much, it is difficult to apply the optical fiber to thecarriage movable. Further, because the UV radiation light source whichhas been generally applied to the ink-jet printer, is a spot lightsource, there is a problem that it is difficult to change the UVradiation to the parallel rays.

[0008] Furthermore, a recording method such as an external surface drumscanning system or a line recording system, has been known, therecording method for moving mainly the recording medium, without movingthe ink jet head or with moving the ink jet head at low speed. In caseof applying the recording method, it is possible to irradiate UVradiation to the UV ink placed on the recording medium rapidly. However,in the case, it is difficult to realize both the small spaced UVradiation light source and the high irradiation of UV radiation to therecording medium. Specially, because it is necessary to irradiate UVradiation to the recording medium for every color of the color print, itis difficult to realize both the small spaced UV radiation light sourceand the high irradiation of UV radiation. Therefore, in case ofirradiating UV radiation having high luminance to the UV ink placed onthe recording medium rapidly, it has been necessary to enlarge theink-jet printer.

SUMMARY OF THE INVENTION

[0009] The present invention is accomplished in order to solve theabove-described problems.

[0010] An object of the present invention is to provide an imagerecording method, an image recording apparatus and energy radiationcurable ink, which can efficiently print less bleeding, high-qualityimages, and reduce a size of the apparatus.

[0011] In order to attain the above-described object, in accordance witha first aspect of the present invention, an image recording method forejecting and placing energy radiation curable ink which is cured whenirradiated with energy radiation according to an ink-jet recordingmethod, irradiating the energy radiation on a recording medium on whichink dots are formed, and printing an image, comprises: ejecting theenergy radiation curable ink to the recording medium from a plurality ofnozzles provided for an ink-jet head, moving the recording medium to theink-jet head relatively, and forming the image; and controlling a rangeto which the energy radiation is irradiated, so as to correspond to arecording width of the ink-jet head.

[0012] In accordance with a second aspect of the present invention, animage recording apparatus for ejecting and placing energy radiationcurable ink which is cured when irradiated with energy radiationaccording to an ink-jet recording method, irradiating the energyradiation on a recording medium on which ink dots are formed, andprinting an image, comprises: an ink-jet head comprising a plurality ofnozzles for ejecting the energy radiation curable ink, the ink-jet headfor ejecting the energy radiation curable ink to the recording medium; arelative moving section for moving the recording medium to the ink-jethead relatively; an energy radiation irradiation section comprising alight emitting section for emitting the energy radiation and anirradiation control section for controlling a range on the recordingmedium to which the energy radiation is irradiated, the energy radiationirradiation section for irradiating the energy radiation to a portion onthe recording medium on which the ink dots are formed; wherein theapparatus prints the image on the recording medium by ejecting theenergy radiation curable ink to the recording medium from the ink-jethead, and moving the recording medium to the ink-jet head relatively bythe relative moving section, and the irradiation control sectioncontrols the range so as to correspond to a recording width of theink-jet head.

[0013] According to the method of the first aspect or the apparatus ofthe second aspect of the present invention, because the energy radiationis irradiated so as to correspond to the recording width of the ink-jethead, it is possible to irradiate the energy radiation to the ink dotsrapidly, and prevent the ink dots from bleeding or expanding on therecording medium. Consequently, it is possible to cure the ink dots withcontrolling a dot diameter or a dot shape of each ink dot, and printhigh-quality images on the recording medium.

[0014] Further, even if the energy radiation is emitted from a deviceoutputting low energy, such as a semiconductor laser or a LED, becausethe range on the recording medium to which the energy radiation isirradiated is controlled so as to correspond to the recording width ofthe ink-jet head, it is possible to net energy amount of the energyradiation irradiated to the ink dots. Consequently, it is possible tocure the ink dots rapidly, and print high-quality images.

[0015] Preferably, in the method of the first aspect of the presentinvention, the energy radiation is emitted from at least one of a laserdevice and a LED, and the irradiating the energy radiation is performedby scanning the recording medium with the energy radiation.

[0016] Preferably, in the apparatus of the second aspect of the presentinvention, the energy radiation irradiation section comprises a scanningsection for scanning the recording medium by irradiating the energyradiation to the recording medium, the light emitting section emits theenergy radiation from at least one of a laser device and a LED, and theirradiation control section controls the range by controlling a portionof the recording medium scanned by the scanning section.

[0017] According to the method or the apparatus, because the energyradiation is emitted from a device such as a laser device or a LED, itis possible to condense the energy radiation and change it to parallelrays easily. Because the energy radiation which is parallel rays isirradiated on the recording medium so as to correspond to the recordingwidth of the ink-jet head, it is possible to easily irradiate the energyradiation having high energy per second and per inch, to the ink dotsimmediately after placed.

[0018] Further, because it is possible to prepare a compact opticalsystem for changing the energy radiation to parallel rays, it ispossible to prepare a compact image recording apparatus which can printhigh-quality images, easily.

[0019] Preferably, in the above-described method, the nozzles arearranged in a line, and the scanning the recording medium with theenergy radiation is performed in a substantially parallel direction to adirection in which the nozzles are arranged.

[0020] Preferably, in the above-described apparatus, the nozzles arearranged in a line, and the scanning section scans the recording mediumwith the energy radiation in a substantially parallel direction to adirection in which the nozzles are arranged.

[0021] According to the method or the apparatus, because the energyradiation is irradiated in the direction of the arrangement of the inkdots which are formed at the substantially same time, it is possible toscan the ink dots formed on the recording medium with the energyradiation within the extremely small time difference. Consequently, itis possible to cure the ink dots substantially equally, and control thedot diameter and the dot shape of each ink dot substantially uniformly.As a result, it is possible to print high-quality images on therecording medium.

[0022] Preferably, in the method of the first aspect of the presentinvention, the moving the recording medium to the ink-jet headrelatively includes moving the recording medium to the ink-jet headrelatively by rotating a cylindrical drum having an external surface onwhich the recording medium is attached.

[0023] Preferably, in the apparatus of the second aspect of the presentinvention, the relative moving section comprises a cylindrical drumhaving an external surface on which the recording medium can beattached, and a driving rotating section for rotating the drum, andmoves the recording medium to the ink-jet head relatively by rotatingthe drum in a condition that the recording medium is attached on theexternal surface of the drum.

[0024] According to the method or the apparatus, it is possible that theimage recording apparatus printing images according to the externalsurface drum scanning system efficiently prints less bleeding,high-quality images on the recording medium. In addition, it is possibleto prepare the compact image recording apparatus.

[0025] Preferably, in the method of the first aspect of the presentinvention, the ink-jet head is a line head, and the moving the recordingmedium to the ink-jet head relatively includes moving the recordingmedium to the ink-jet head relatively by carrying the recording mediumin a vertical direction to the line head.

[0026] Preferably, in the apparatus of the second aspect of the presentinvention, the ink-jet head is a line head, and the relative movingsection moves the recording medium to the ink-jet head relatively bycarrying the recording medium in a vertical direction to the line head.

[0027] According to the method or the apparatus, it is possible that theimage recording apparatus printing images according to the linerecording system efficiently prints less bleeding, high-quality imageson the recording medium. In addition, it is possible to prepare thecompact image recording apparatus.

[0028] Preferably, in the method of the first aspect of the presentinvention, the nozzles are arranged so as to form the ink dots having adensity of 300 dpi or higher on the recording medium when irradiatingthe energy radiation curable ink therefrom one time.

[0029] Preferably, in the apparatus of the second aspect of the presentinvention, the nozzles are arranged so as to form the ink dots having adensity of 300 dpi or higher on the recording medium when irradiatingthe energy radiation curable ink therefrom one time.

[0030] According to the method or the apparatus, because the ink dotshaving the density of 300 dpi or higher can be formed on the recordingmedium when the energy radiation curable ink is ejected one time, it ispossible to increase net energy of the energy radiation irradiated tothe ink dots. Consequently, it is possible to print images havinghigh-resolution rapidly without the ink dots expanding or bleeding onthe recording medium.

[0031] Preferably, in the method of the first aspect of the presentinvention, a wavelength of the energy radiation is within a range from250 to 450 nm or 800 nm or longer.

[0032] Preferably, in the apparatus of the second aspect of the presentinvention, a wavelength of the energy radiation emitted from the lightemitting section is within a range from 250 to 450 nm or 800 nm orlonger.

[0033] According to the method or the apparatus, it is possible to applya well-known material or a well-known device which can be got easily, tothe energy radiation curable ink or the light emitting section foremitting the energy radiation, respectively. Consequently, it ispossible to prepare the energy radiation curable ink or the imagerecording apparatus easily, at low cost.

[0034] Preferably, in the method of the first aspect of the presentinvention, a luminance of the energy radiation irradiated to therecording medium is 1000 mW/cm² or higher.

[0035] Preferably, in the apparatus of the second aspect of the presentinvention, the energy radiation irradiation section comprises acondenser for condensing the energy radiation, and the condensercondenses the energy radiation so that a luminance of the energyradiation irradiated to the recording medium is 1000 mW/cm² or higher.

[0036] According to the method or the apparatus, because the luminanceof the energy radiation is 1000 mW/cm² or higher when scanning the rangeof the recording medium, it is possible to prevent the energy radiationcurable ink from bleeding or the like on the recording medium, and printhigh-quality images.

[0037] Preferably, in the above-described method, a time after theenergy radiation curable ink is placed on the recording medium until theink dots are scanned and irradiated with the energy radiation is withina range from 0.02 to 500 ms.

[0038] Preferably, in the above-described apparatus, the scanningsection scans the recording medium with the energy radiation so that theink dots are irradiated with the energy radiation after 0.02 to 500 mssince the energy radiation curable ink is placed on the recordingmedium.

[0039] According to the method or the apparatus, the energy radiation isirradiated to the ink dots at the time the energy radiation curable inkplaced on the recording medium properly expands on the recording medium,by leveling as the ink dots. Consequently, it is possible to prevent theink dots from bleeding on the recording medium, and print high-qualityimages.

[0040] Preferably, in the method of the first aspect of the presentinvention, a speed of moving the recording medium to the ink-jet headrelatively is within a range from 0.3 to 200 m/s.

[0041] Preferably, in the apparatus of the second aspect of the presentinvention, the relative moving section changes a relative position ofthe recording medium to the ink-jet head at a speed within a range from0.3 to 200 m/s.

[0042] According to the method or the apparatus, it is possible to printimages efficiently, without enlarging the relative moving section formoving the recording medium relatively. Consequently, it is possible toprepare the compact image recording apparatus which can print imageefficiently.

[0043] In accordance with a third aspect of the present invention,energy radiation curable ink used for the image recording method asdescribed above, comprises: a polymerizable composition to form apolymer compound through polymerization reaction, an initiator forinitiating the polymerization reaction when irradiated with the energyradiation, and a color material for coloring the energy radiationcurable ink, wherein the initiator initiates the polymerization reactionwhen irradiated with the energy radiation having a wavelength which iswithin a range from 250 to 450 nm or 800 nm or longer.

[0044] According to the ink of the third aspect of the presentinvention, it is possible to apply a well-known material or a well-knowndevice which can be got easily, to the energy radiation curable ink orthe light emitting section for emitting the energy radiation,respectively. Consequently, it is possible to prepare the energyradiation curable ink or the image recording apparatus easily, at lowcost.

[0045] Preferably, in the ink of the third aspect of the presentinvention, amount of addition of the initiator is within a range from0.1 to 3 wt %.

[0046] According to the ink, when the energy radiation having the highluminance which is 1000 mW/cm² or higher is irradiated to the ink dots,a polymer compound is generated from the ink dots, at a proper molecularweight distribution. Consequently, it is possible to cure the ink dotwith sufficient strength and adhesiveness to the recording medium. As aresult, it is possible to print images having high durability, frictionresistence or the like.

[0047] Preferably, the ink of the third aspect of the present invention,further comprises an initiation auxiliary for giving excitation energyto the initiator when irradiated with the energy radiation, and makingthe initiator initiate the polymerization reaction.

[0048] According to the ink, even if the initiator does not absorb theenergy radiation emitted from the light emitting section although theinitiator is selected by reasons of the property such as strength of thecured ink dots, because the initiation auxiliary is properly selectedand added in the ink, it is possible to cure the ink dots efficiently.Consequently, it is possible to print high-quality images having highstrength according to various recording mediums or uses.

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The present invention will become more fully understood from thedetailed description given hereinafter and the accompanying drawinggiven by way of illustration only, and thus are not intended as adefinition of the limits of the present invention, and wherein:

[0050]FIG. 1 is a top view for schematically showing an ink-jet printer1 according to a first embodiment of the present invention;

[0051]FIG. 2A is a vertical front view of a main part of the ink-jetprinter 1 according to the first embodiment, and FIG. 2B is a verticalside view of the main part;

[0052]FIG. 3A is a vertical top view of the main pert of the ink-jetprinter 1 according to a second embodiment, and FIG. 3B is a verticalside view of the main part;

[0053]FIG. 4A is a vertical front view of the main part of the ink-jetprinter 1 according to a third embodiment, and FIG. 4B is a verticalside view of the main part;

[0054]FIG. 5A is a vertical front view of the main part of the ink-jetprinter 1 according to another example of the first embodiment, and FIG.5B is a vertical top view of the main part; and

[0055]FIG. 6 is a vertical front view of the main part of the ink-jetprinter 1 of another example of the third embodiment.

PREFERRED EMBODIMENTS OF THE INVENTION

[0056] [First Embodiment]

[0057] Hereinafter, an ink-jet printer 1 which is an image recordingapparatus for ejecting photo-curable ink having a property to be curedwhen irradiated with UV radiation as a kind of energy radiation curableink, to a recording medium, and printing images, will be explained byway of example of the first embodiment of the present invention, withreference to the figures.

[0058] The ink-jet printer of the present invention is not limited toone using the photo-curable ink. The ink-jet printer may use energyradiation curable ink having a property to be cured when irradiated withenergy radiation such as infrared radiation, visible radiation, electronrays, X-rays or the like. Herein, the energy radiation means energyradiation in a wide sense. The energy radiation includes not only onehaving a property of electrically separating air, but also one includingan electromagnetic wave such as infrared radiation, visible radiation,UV radiation, electron rays or the like as described above.

[0059] The ink-jet printer 1 according to the first embodiment, printsimages according to a capstan system for ejecting the photo-curable inkfrom an ink-jet head 2 with moving both the ink-jet head 2 and arecording medium P, and thereby forming an image on the recording mediumP.

[0060] The ink-jet printer 1 comprises a relative moving section (whichis not shown in figures), a printing section 20, a light irradiationsection 23, a guide rail 50, and a controller (which is not shown infigures) for controlling each section, as shown in FIG. 1 and FIGS. 2Aand 2B.

[0061] The relative moving section carries the recording medium Pthrough a space under the carriage 21, in a direction of an arrow “S” (Sdirection) in FIG. 1 or FIG. 2B, at the time of the movement of thecarriage 21. Thereby, the recording medium P moves to the ink-jet heads2, 2 and so on, relatively, Preferably, the speed the relative movingsection carries the recording medium P is within a range from 0.3 to 200m/s. The speed less than 0.3 m/s causes a problem that the efficiency ofprinting images on the recoding medium P is lowered. On the other hand,the speed more than 200 m/s causes a problem that it is required toenlarge the relative moving section, and it is impossible to prepare thecompact ink-jet printer 1.

[0062] The printing section 20 comprises ink-jet heads 2, 2 and so on,the carriage 21 and so on. A plurality of nozzles for ejecting thephoto-curable ink to form ink dots on the recording medium P, areprovided on a nozzle surface 2 a of each ink-jet head 2, which is asurface to the recording medium P. A plurality of ink-jet heads 2, 2 andso on, and a plurality of light irradiation sections 23, 23 and so onare provided on the carriage 21, in a form that the ink-jet heads 2, 2and so on and the light irradiation sections 23, 23 and so on arearranged alternately in the “A” direction, according to colors (forexample, yellow, magenta, cyan, black) of the ink ejected to therecording medium P.

[0063] The carriage 21 has a structure movable in the direction (“A”direction) of the arrow “A” in FIGS. 1 or 2A, which is a horizontaldirection along the guide rail 50. A linear encoder 51 is provided forthe guide rail 50. The controller can obtain the present position of thecarriage 21, on the basis of data outputted from the linear encoder 51.

[0064] A plurality of nozzles are arranged on the nozzles surface 2 a ofthe ink-jet head 2, which is turned to the recording medium P. Further,the nozzles are arranged so as to be substantially parallel to the “S”direction when contained in the carriage 21. Furthermore, the nozzlesare arranged so as to form ink dots on the recording medium P whenejecting the photo-curable ink of the length “1” shown in FIG. 2B, onetime.

[0065] Herein, the recording width of the ink-jet head 2 is a length inthe direction that the nozzles are arranged, of the range on which theink dots can be formed without the ink-jet heads 2 moves. That is, therecording width of the ink-jet head 2 is the length “1” in FIG. 2Baccording to the embodiment.

[0066] Each nozzle is formed so as to connect to an ejecting sectionwhich is not shown in figures and which is contained in an inside of theink-jet head 2. When the ejecting section drives, the photo-curable inkis ejected from each nozzle. Preferably, the distance between theplurality of nozzles provided on the nozzle surface 2 a is determined soas to form the ink dots having the density of 300 dpi (dots per inch) orhigher, on the recording medium P, when the photo-curable ink is ejectedfrom the nozzles one time. Because the plurality of nozzles are providedat the distance, when the printing section 20 scans the recording mediumP one time, by moving the recording medium P with a sub carryingsection, and moving the carriage 21 in the “A” direction, it is possibleto print images having a sufficient resolution on the recording mediumP.

[0067] The light irradiation section 23 is an energy radiationirradiation section. The light irradiation section 23 comprises a lightemitting section 231, a scanning section 232, a collimator (which is notshown in figures) and so on. When the light irradiation section 23 scansthe range of the reading medium P, on which the ink dots are formed, byUV radiation, the ink dots are cured.

[0068] The light emitting section 231 comprises a well-known lightemitting device which is a laser element (laser) such as a LED (Lightemitting diode), a semiconductor laser element or the like.

[0069] Herein, the wavelength of UV radiation emitted from the lightemitting section 231 is properly selected within a wavelength by whichthe photo-curable ink ejected from the ink-jet heads 2, 2 and so on canbe cured rapidly. Preferably, the wavelength of UV radiation is 250 nmor longer. Because the wavelength of the light emitted from the lightemitting section 231 is determined as described above, it is possible toapply a well-known light emitting device and the photo-curable inkhaving the following composition to the ink-jet printer 1, and printhigh-quality images on the recording medium P at low cost. For example,in case the wavelength of the UV radiation is shorter than 250 nm, it isextremely difficult to construct the optical system, that is thecollimator, the scanning section 232 or the like, of materialstransmitting the UV radiation having the wavelength. Therefore, the costrequired to prepare or maintain the ink-jet printer 1, may increase.

[0070] Further, in case the energy radiation emitted from the lightemitting section 231 is visible radiation, because an initiator or aninitiation auxiliary (which will be explained as follows) included inthe photo-curable ink absorbs the visible radiation, the initiator orthe initiation auxiliary emits coloring. Therefore, there occurs aproblem of inhibiting the color tone of the photo-curable ink. In caseonly ink having a strong color tone like black is applied to thephoto-curable ink, like a black and white printing, if the photo-curableink includes the initiator or the initiation auxiliary which absorbsvisible radiation having a wavelength of 450 nm or shorter, the qualityof the image is affected by the visible radiation. Accordingly, in thecase, the visible radiation having the wavelength of 450 nm or shorter,can be applied as the energy radiation.

[0071] The collimator condenses the UV radiation emitted from the lightemitting section 231, and changes it to parallel rays to make it reachthe scanning section 232. Herein, preferably, the collimator isdetermined so as to condense the UV radiation and change it to parallelrays, so that luminance of the UV radiation is 1000 mW/m² or higher whenthe UV radiation reaches the recording medium P. Because the luminanceof the UV radiation on the recording medium P is determined as describedabove, it is possible to cure the ink dots formed on the recordingmedium P rapidly, prevent the ink dots from bleeding or expandingunnecessarily, and form high-quality images on the recording medium P.

[0072] More preferably, the above-described collimator condenses the UVradiation so that the intensity of the UV radiation when reaching therecording medium P is 3000 mW/m² or higher. Because the intensity of theUV radiation on the recording medium P is 3000 mW/m² or higher, if theamount of addition of the initiator included in the photo-curable ink isreduced, it is possible to cure the photo-curable ink on the recordingmedium P rapidly, and prevent the ink dots from bleeding or expandingunnecessarily. Because a well-known initiator is expensive, when theamount of addition of the initiator in the photo-curable ink is reduced,and the photo-curable ink is cured rapidly, it is possible to fromhigh-quality images on the recording medium P at low costs.

[0073] According to the embodiment, the scanning section 232 functionsas the irradiation control section. The scanning section 232 comprises agalvanometer mirror 232 a and a motor which is not shown in figures. Thegalvanometer mirror 232 a deflects an angle to the light emittingsection 231 by the motor, periodically, changes the optical path of theUV radiation emitted from the light emitting section 231, and irradiatesthe UV radiation to the recording medium P. Further, the scanningsection 232 controls the angle range to which the galvanometer mirror232 a irradiates the UV radiation, and controls the range of therecording medium P, to which the UV radiation is irradiated. Thegalvanometer mirror 232 a may drive by not the motor but an oscillator.

[0074] The width (the length in the “A” direction in FIG. 2A) of therange on the recording medium P, to which the light irradiation section23 irradiates the UV radiation is determined on the basis of thediameter of the UV radiation condensed by the collimator.

[0075] The length (the length in the “S” direction in FIG. 2B) of theabove-described range is determined on the basis of the range withinwhich the galvanometer mirror 232 a deflects the UV radiation.

[0076] The shape of the above-described range is determined so as tocorrespond to the range in which the ink dots are formed when theink-jet heads 2 eject the ink to the recording medium P one time,without moving. More specifically, the shape of the range is determinedso that the ink dots are formed on the recording medium P, irradiatedwith the UV radiation certainly and rapidly, and cured by using theenergy of the UV radiation efficiently. Specially, preferably, thelength of the range is determined to be the substantially same as thelength “1” which is the recording wide of the ink-jet heads 2, with theview of using the energy of the UV radiation efficiently.

[0077] The position of the range on the recording medium P to which thelight irradiation section 23 irradiates the UV radiation, is determinedso that the ink dots are irradiated with the UV radiation immediatelyafter formed by moving the carriage 21.

[0078] The period and the timing of the deflection of the UV radiationby the galvanometer mirror 232 a, is determined so that the time afterthe photo-curable ink ejected from the ink-jet heads 2 are placed on therecording medium P until the photo-curable ink is irradiated with the UVradiation is within a range from 0.02 to 500 ms. In case the time is0.02 ms or shorter, because the photo-curable ink placed on therecording medium P is cured without leveling sufficiently as an ink dot,the diameter of the dot is extremely small. Therefore, there occurs aproblem that the quality of the image formed on the recording medium Pis lowered, the adhesiveness of the ink dot on the recording medium P islowered, and the strength of the image is lowered. On the other hand, incase the time is 500 ms or longer, because the photo-curable ink bleedson the recording medium P or the like, the quality of the image formedon the recording medium P is lowered. Accordingly, for theabove-described reasons, the period and the timing of the deflection ofthe UV radiation by the galvanometer mirror 232 a, is determined inconsideration of the dot diameter required for the ink dot, the movingspeed of the carriage 21, the property of the photo-curable ink, thepositional relation between the ink-jet heads 2 and the galvanometermirror 232 a, or the like, as the occasion may demand.

[0079] Preferably, the direction of scanning with UV radiation by thegalvanometer mirror 232 a is substantially parallel to the “S” directionin which the nozzles are arranged. Because the scanning direction isdetermined as described above, it is possible to scan the row of inkdots formed on the recording medium P at the substantially same time,with UV radiation. Therefore, it is possible to minimize the differenceof time after each ink dot is formed on the recording medium P until itis irradiated with the UV radiation. Accordingly, because each ink dotis cured equally, it is possible to control the dot diameter and theshape of the dot, and improve the quality of the image.

[0080] The scanning section 232 may use not only the galvanometer mirror232 a but also a polygon mirror in order to change the optical path ofthe UV radiation emitted from the light emitting section 231. However,preferably, in the ink-jet printer 1 of the present invention, thescanning section 232 is composed so as to change the optical path of theUV radiation with the galvanometer mirror 232 a, for following reasons.

[0081] The optical system to which the galvanometer mirror 232 a isapplied, can be made smaller than an optical system to which the polygonmirror is applied. In the ink-jet printer 1, because the lightirradiation section 23 is provided for the carriage 21, it is preferableto apply the galvanometer mirror 232 a to the scanning section 232, inorder to provide the light and compact carriage 21.

[0082] However, there is a problem that the galvanometer mirror 232 a isless accurate than the polygon mirror or the like, when deflecting theoptical path. However, in the ink-jet printer 1, the diameter of UVradiation is larger than the diameter of the ink dot. Therefore, in caseof scanning the ink dot with UV radiation in order to cure the ink dot,the high accuracy is not required when deflecting UV radiation.Accordingly, it is preferable to apply the galvanometer mirror 232 a tothe ink-jet printer 1 of the preset invention.

[0083] Next, the photo-curable ink applicable to the ink-jet printer 1according to the present invention will be described.

[0084] The photo-curable ink is preferably blended so as to adjust itsviscosity at 25° C. to 6 to 500 mPa.s and surface tension to 20 to 35mN/m, so that the ink dots after placed on the recording medium P areappropriately leveled and exhibit adhesiveness. It is also preferable tocontrol temperature of the photo-curable ink at the time of ejectionthereof out from the ink-jet head 2 so that the ink exhibits a viscosityof 6 to 20 mPa.s in view of properly controlling the dot diameter on therecording medium P and preventing clogging of the ink within the nozzle.

[0085] It is also preferable to supply the photo-curable ink to theink-jet head 2 after being filtered through a filter having a pore sizeof at least 2 μm or smaller, and more preferably 1 μm or smaller, so asto remove coarse particles.

[0086] Beside being furnished with the aforementioned physicalproperties, the photo-curable ink is composed so as to contain at leasta polymerizable composition and an initiator, beside a color materialfor coloring, in order to allow itself to cure through polymerizationreaction when irradiated with UV radiation from the light irradiationsection 23. In addition, the photo-curable ink optionally contain aninitiation auxiliary, surfactant, polymerization inhibitor, antistaticagent or the like. Depending of the wavelength of UV radiation to beirradiated, a sensitization dye is preferably added as an initiationauxiliary.

[0087] Specific compositions of the photo-curable ink will be explainedbelow.

[0088] The polymerizable composition refers to a material which curesthe photo-curable ink by forming a polymer through polymerization whenirradiated with UV radiation. Publicly-known polymerizable compositionsinclude photo-radical-polymerizable composition which polymerizes basedon radical reaction under light irradiation, and cationic polymerizablecomposition based on a cationic polymerization system which polymerizesbased on cationic species as reactive species. These are described forexample in various patent documents such as Japanese Laid-Open PatentPublication No. Tokukai-hei 7-159983, Japanese Examined PatentPublication No. Tokuko-hei 7-31399, Japanese Laid-Open PatentPublication No. Tokukai-hei 8-224982, Japanese Laid-Open PatentPublication No. Tokukai-hei 10-863, and Japanese Patent Application No.Tokugan-hei 7-231444. Recently, a photo-curable resin based on aphoto-cationic-polymerization system, sensitized up into a longerwavelength region from the visible radiation region, is also disclosedin Japanese Laid-Open Patent Publication Nos. Tokukai-hei 6-43633, andTokukai-hei 8-324137, and so on.

[0089] The radical-polymerizable composition is a compound having anethylene-base unsaturated bond capable of radical polymerization, whereany compounds are allowable so far as they have at least oneethylene-base unsaturated bond capable of radical polymerization withintheir molecules. Further, the radical-polymerizable composition includesthose having any chemical structures of monomer, oligomer, polymer orthe like. As the polymerizable composition, the radical-polymerizablecomposition may be used independently, or in combination of two or morespecies in an arbitrary ratio of mixing in order to improve some targetcharacteristics.

[0090] Specific examples of the compound having a radical-polymerizable,ethylene-base unsaturated bond include unsaturated carboxylic acids suchas acrylic acid, methacrylic acid, itaconic acid, crotonic acid,isocrotonic acid, maleic acid, as well as salts, ester, urethane, amideand anhydride thereof; acrylonitrile; styrene; and variousradical-polymerizable compositions such as unsaturated polyester,unsaturated polyether, unsaturated polyamide, and unsaturated urethane.

[0091] Specific examples of the radical-polymerizable compositionshaving an ethylene-base unsaturated bond include methacrylic derivativesenumerated below. The methacrylic derivatives include acrylic acidderivatives such as 2-ethylhexylacrylate, 2-hydroxyethylacrylate,butoxyethyl acrylate, carbitol acrylate, cyclohexyl acrylate,tetrahydrofurfuryl acrylate, benzylacrylate,bis(4-acryloxy-polyethoxyphenyl)propane, neopentyl glycol diacrylate,1,6-hexanediol diacrylate, ethylene glycol diacrylate, diethylene glycoldiacrylate, triethylene glycol diacrylate, tetraethylene glycoldiacrylate, polyethylene glycol diacrylate, polypropylene glycoldiacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate,dipentaerythritol tetraacrylate, trimethylolpropane triacrylate,tetramethylolmethane tetraacrylate, oligoester acrylate, N-methylolacrylamide, diacetone acrylamide, epoxy acrylate; methyl methacrylate,n-butyl methacrylate, 2-ethylhexyl methacrylate, laryl methacrylate,allyl methacrylate, glycidyl methacrylate, benzyl methacrylate,dimethylaminomethyl methacrylate, 1,6-hexanediol dimethacrylate,ethylene glycol dimethacrylate, triethylene glycol dimethacrylate,polyethylene glycol dimethacrylate, polypropylene glycol dimethacrylate,trimethylolethane trimethacrylate, trimethylolpropane trimethacrylate,and 2,2-bis(4-methacryloxypolyethoxyphenyl)propane.

[0092] Other radical-polymerizable compounds include derivatives ofallyl compounds such as allyl glycidyl ether, diallyl phthalate andtriallyl trimellitate. More specifically, they are possiblypublicly-known, radical-polymerizable or crosslinkable monomers,oligomers or polymers typically described in “Kakyozai Handobukku(Handbook on Crosslinking Agent)” (edited by Shinzo Yamashita, publishedby Taiseisha Co., Ltd., 1981); “UV•EB Koka Handobukku—Genryo-Hen(Handbook on UV/EB Curing—Source Material Series)” (edited by KiyomiKato, published by Kobunshi Kanko-Kai, 1985); “UV•EB Koka Gijutsu no Oyoto Shijo (Applications and Market of UV/EB Curing Technology)”, p.79,(edited by RadTech Japan, published by CMC Publishing Co., Ltd., 1989);“Poriesuteru Rejin Handobukku (Handbook on Polyester Resin)” (written byEiichiro Takiyama, published by The Nikkan Kogyo Shimbun, Ltd., 1988).

[0093] Amount of addition of the radical-polymerizable compositionrelative to the photo-curable ink is preferably selected within a rangefrom 1 to 97 wt %. The amount of addition of the radical-polymerizablecomposition less than 1 wt % may inhibit rapid curing of thephoto-curable ink which should be induced by UV irradiation, and thusmay inhibit control of the dot-forming system. The amount of addition ofthe radical-polymerizable composition exceeding 97 wt % may inhibitsatisfactory coloring by the color material, and thus may degrade colorreproducibility of images possibly produced on the recording medium P.The amount of addition of the radical-polymerizable composition relativeto the photo-curable ink is preferably selected within a range from 30to 95 wt %.

[0094] As the polymerizable composition based on cationic polymerizationsystem, preferably applicable examples include epoxy-type, UV-curableprepolymers and monomers having two or more epoxy groups within a singlemolecule, where both of them cause polymerization based on cationicpolymerization. Examples of such prepolymers include alicyclicpolyepoxides, polyglycidyl esters of polybasic acid, polyglycidyl ethersof polyhydric alcohol, polyglycidyl ethers of polyoxyalkylene glycol,polyglycidyl ethers of aromatic polyol, hydrogenated compounds ofpolyglycidyl ethers of aromatic polyol, urethane polyepoxy compounds andepoxidized polybutadienes. As the polymerizable composition, theseprepolymers and monomers can be used independently or in a mixed form oftwo or more species.

[0095] Other examples of the cationic polymerizable compositioncontained in the photo-curable resin based on cationic polymerizationsystem typically include (1) styrene derivatives, (2) vinylnaphthalenederivatives, (3) vinyl ethers and (4) N-vinyl compounds, as enumeratedbelow:

[0096] (1) Styrene Derivatives

[0097] styrene, p-methylstyrene, p-methoxystyrene, β-methylstyrene,p-methyl-β-methylstyrene, α-methylstyrene, p-methoxy-β-methylstyrene,etc.;

[0098] (2) Vinylnaphthalene Derivaties

[0099] 2-vinylnaphthalene, α-methyl-2-vinylnaphthalene,β-methyl-2-vinylnaphthalene, 4-methyl-2-vinylnaphthalene,4-methoxy-2-vinylnaphthalene, etc.;

[0100] (3) Vinyl Ethers

[0101] isobutyl vinyl ether, ethyl vinyl ether, phenyl vinyl ether,p-methylphenyl vinyl ether, p-methoxyphenyl vinyl ether, α-methylphenylvinyl ether, β-methylisobutyl vinyl ether, β-chloroisobutyl vinyl ether,etc.; and

[0102] (4) N-vinyl Compounds

[0103] N-vinylcarbazole, N-vinylpyrolidone, N-vinylindole,N-vinylpyrrole, N-vinylphenothiazine, N-vinylacetanilide, N-vinylethylacetamide, N-vinylsuccinimide, N-vinylphthalimide, N-vinylcaprolactam,N-vinylimidazole, etc.

[0104] Content of the polymerizable composition in the cationicpolymerization system to the photo-curable ink is preferably selectedwithin a range from 1 to 97 wt %. The amount of addition of thecation-polymerizable composition less than 1 wt % may inhibit rapidcuring of the photo-curable ink which should be induced by UVirradiation, and thus may inhibit control of the dot-forming system. Theamount of addition of the radical-polymerizable composition exceeding 97wt % may inhibit satisfactory coloring by the color material, and thusmay degrade color reproducibility of images possibly produced on therecording medium P. The amount of addition of the cation-polymerizablecomposition relative to the photo-curable ink is preferably selectedwithin a range from 30 to 95 wt %.

[0105] The photo-curable ink is added with an initiator for initiatingpolymerization reaction of the polymerizable composition under UVirradiation. The initiators respectively suited for either of theradical-polymerizable composition and cation-polymerizable compositionare applied.

[0106] Publicly-known initiators applicable to the photo-curable inkcontaining the radical-polymerizable composition include aryl alkylketone, oxime ketone, acylphosphine oxide, acylphosphonate, thiobenzoicacid S-phenyl, titanocene, aromatic ketone, thioxanthone, benzyl andquinone derivatives and ketocoumarins.

[0107] Of these initiators, acylphosphine oxide and acylphosphonate arepreferable as those for the radical-polymerization system. Theseinitiators specifically have a high sensitivity to UV radiation, andactive species generated therefrom by UV irradiation have a considerablylow absorbance as compared with that of the initiators beforeirradiation. Because the photo-curable ink ejected out from the ink-jethead 2 and placed on the recording medium P have a thickness of as largeas 5 to 15 μm, initiators such as acylphosphine oxide andacylphosphonate are preferable in view of rapid curing of the innerportion of the photo-curable ink placed on the recording medium P.

[0108] For this reason, specific examples of preferred initiators forthe radical polymerization system includebis-(2,4,6-trimethylbenzoyl)-phenylphosphine oxide andbis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide.

[0109] For the case where the initiators having a high UV sensitivityand also having a weak odor are to be selected, preferable examplesthereof include 1-hydroxy-cyclohexyl-phenyl-ketone,2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropane-1-one,2-hydroxy-2-methyl-1-phenylpropane-1-one and2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1.

[0110] For the case where the initiators having a high UV sensitivityand also having a polymerization property less likely to be inhibited byoxygen in the air are to be selected, preferable examples thereofinclude a combination of2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1 with1-hydroxy-cyclohexyl phenyl ketone, a combination of1-hydroxy-cyclohexyl-phenyl-ketone with benzophenone, combinations of2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropane-1-one or2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropane-1-one withdiethylthioxanthone or isopropylthioxanthone, a combination ofbenzophenone with acrylic acid derivative having a tertiary amino group,and addition of a tertiary amine.

[0111] The initiator is preferably added into the photo-curable ink, inan amount of 0.1 to 3 wt %. The amount of addition of the initiator lessthan 0.1 wt % may make it difficult to control diameter or shape of theink dots because the photo-curable ink placed on the recording mediumcannot rapidly be cured. The amount of addition exceeding 3 wt % mayundesirably increase the number of polymerization nuclei because theconcentration of reactive species generated during the polymerizationreaction becomes considerably high, and this consequently inhibitspolymerization of the polymerizable composition in a large degree ofpolymerization and thus considerably lowers strength of the curedphoto-curable ink or adhesiveness on the recording medium P.

[0112] It is to be noted that the amount of addition described in theabove is lower than that for the photo-curable ink (5 to 15 wt %) whichhas been applied to the conventional ink-jet printers using a highpressure mercury lamp or metal halide lamp as the light emittingsection. This is because luminance of UV radiation to be irradiated tothe ink dots in the present invention is as high as 1,000 mW/cm² and isconsiderably higher than that in the conventional cases. Therefore, ifthe initiator is added in an amount same as that applied to theconventional ink-jet printers, the ink dots irradiated by such a highluminance of UV radiation initiates a polymerization reaction only toproduce polymer compounds having considerably low molecular weights, andthe strength and adhesiveness to the recording medium P of thus curedphoto-curable ink become low as a consequence.

[0113] It is to be noted that two or more initiators can be usedtogether in the present invention. Besides the compounds shown in theabove, the initiator may also be any of the publicly-known compoundsdescribed for example in “UV EB Koka Gijutsu no Oyo to Shijo(Applications and Market of UV/EB Curing Technology)” (published by CMCPublishing Co., Ltd., compiled by Yoneho Tabata/edited by RadTechJapan).

[0114] On the other hand, for the case where the cation-polymerizablecomposition is applied to the photo-curable ink, it is allowable toapply a photo-acid generator as the initiator. Available photo-acidgenerators typically include chemical amplification photo-resist andcompounds used for photo-cationic polymerization. The compoundsapplicable herein are such as those described in “Imejingu-Yo YukiZairyo (Organic Materials for Imaging)”, edited by The Japanese ResearchAssociation for Organic Electronics Materials, published by Bun-ShinShuppan K. K., 1993, p.187-192.

[0115] For the case where the cation polymerization compound is appliedto the photo-curable ink, compounds suitable for the initiator can beclassified into five following groups.

[0116] A first group include aromatic onium salts which comprise cationssuch as diazonium, ammonium, iodonium, sulfonium and phosphonium cationstypically expressed by formulae (1) to (14), and anions such as B(C₆F₅)₄⁻, PF₆ ⁻, AsF₆ ⁻, SbF₆ ⁻ and CF₃SO₃ ⁻. As the initiators belonging tothe first group, those having borate as a counter ion is particularlypreferable in view of exhibiting an excellent acid generating ability.

[0117] A second group include sulfonated compounds typically expressedby formulae (15) to (25) These compounds can generate sulfonic acid ionunder UV irradiation.

[0118] A third group includes halogenated compounds typically expressedby formulae (26) to (32). These compounds can generate hydrogen halideunder UV irradiation.

[0119] A fourth group includes iron-allene complexes typically expressedby formulae (33) and (34).

[0120] A fifth group includes titanocenes. “Titanocenes” is a generalnomenclature for compounds having a molecular skeleton in which one ortwo cyclopentadienyl ligands are coordinated to a titanium atom.Specific examples include bis-cyclopentadienyl-Ti-dichloride,di-cyclopentadienyl-Ti-bisphenyl,di-cyclopentadienyl-Ti-bis-2,3,4,5,6-pentafluorophen-1-yl,di-cyclopentadienyl-Ti-bis-2,3,5,6-tetrafluorophen-1-yl,di-cyclopentadienyl-Ti-bis-2,4,6-trifluorophen-1-yl,di-cyclopentadienyl-Ti-bis-2,6-difluorophen-1-yl,di-cyclopentadienyl-Ti-bis-2,4-difluorophen-1-yl,di-methylcyclopentadienyl-Ti-bis-2,3,4,5,6-pentafluorophen-1-yl,di-methylcyclopentadienyl-Ti-bis-2,3,5,6-tetrafluorophen-1-yl,di-methylcyclopentadienyl-Ti-bis-2,4-difluorophen-1-yl,bis(cyclopentadienyl)-bis(2,6-difluoro-3-(pyr-1-yl)phenyl)titanium(IRUGACURE784: product of CIBA Specialty Chemicals, K.K.), while beingnot limited thereto.

[0121] The initiation auxiliary is a substance which acts as asensitization dye for giving energy to the initiator and raisinggeneration efficiency of radical or acid from the initiator through anymechanisms of electron donation, electron attraction, heat generation orthe like under UV irradiation, and is used in combination with theinitiator.

[0122] Publicly-known combinations of the initiator and initiationauxiliary applied to radical-polymerizable composition include acombination of peracid ester as the initiator with any initiationauxiliary of xanthene, thioxanthone dye, ketocoumarin and thiopyryliumsalt; and a combination of onium salt such as diphenyliodonium salt asthe initiator with thioxanthene dye as the initiation auxiliary.

[0123] For the case where titanocenes are applied tocation-polymerizable composition as the initiator, it is possible toapply an initiation auxiliary which can allow the titanocens to besensitized from the visible radiation region to near-infrared regioncorresponding to lasers or LEDs, and examples of the initiationauxiliary include cyanine, phthalocyanine, merocyanine, porphyrin, spirocompounds, ferrocene, fluorene, fulgide, imidazole, perilene, phenazine,phenothiazine, polyene, azo compounds, diphenylmethane,triphenylmethane, polymethineacrydine, coumarin, ketocoumarin,quinacridone, indigo, stylyl, pyrylium compounds, pyromethene compounds,pyrazolotriazole compounds, benzothiazole compounds, barbituric acidderivatives, and thiobarbituric acid derivatives.

[0124] As the initiation auxiliary used in combination with titanocene,compounds described in European Patent No. 568,993, U.S. Pat. Nos.4,508,811 and 5,227,227, and Japanese Laid-Open Patent Publication Nos.Tokukai 2001-125255 and Tokukai-hei 11-271969 are also applicable.Specific examples of combinations of titanocenes as thephoto-polymerization initiator with initiation auxiliary include thosedescribed in Japanese Laid-Open Patent Publication Nos. Tokukai2001-125255 and Tokukai-hei 11-271969.

[0125] The initiation auxiliary is used for the case where the initiatorapplied to the photo-curable ink does not have an absorbance whichensures sufficient absorption of UV radiation irradiated from the lightirradiation section 23. That is, for the case where the initiator isselected considering strength of the cured ink dots and adhesivenessthereof on the recording medium P, but the initiator does not absorb UVradiation possibly emitted from the light emitting portion 231,application of the initiation auxiliary can successfully cure the inkdots. Application of the initiation auxiliary to the photo-curable inkas described in the above makes it possible to print high-quality,high-strength images corresponding to a variety of recording media andapplications.

[0126] As for the initiation auxiliary, besides the compounds describedin the above, it is also allowable to apply any substances which arepublicly known to function as a sensitization dye in the literaturessuch as “Kobunshi Tenkazai no Kaihatsu Gijutsu (Technology of DevelopingPolymer Additives)”, published by CMC Publishing Co., Ltd, compiled byYasukazu Ohkatsu. It is to be noted that the initiation auxiliary can beassumed as a component which composes a part of the initiator.

[0127] In order to color the photo-curable ink, a color material isadded to the photo-curable ink by dispersion as described in the above.Applicable color materials are such as those soluble or dispersible intothe major component of the polymerizable composition, and pigment ispreferable from the viewpoint of light resistance. While thoseenumerated below are applicable as the pigment, the pigment applicableto the present invention is by no means limited thereto:

[0128] C.I. Pigment Yellow-1, 3, 12, 13, 14, 17, 81, 83, 87, 95, 109,42, 74, 128, 185;

[0129] C.I. Pigment Orange-16, 36, 38;

[0130] C.I. Pigment Red-5, 22, 38, 48:1, 48:2, 48:4, 49:1, 53:1, 57:1,63:1, 144, 146, 185, 101, 2, 12, 9, 122, 184, 188;

[0131] C.I. Pigment Violet-19, 23;

[0132] C.I. Pigment Blue-15:1, 15:3, 15:4, 18, 60, 27, 29;

[0133] C.I. Pigment Green-7, 36;

[0134] C.I. Pigment White-6, 18, 21 and other organic white pigments;and

[0135] C.I. Pigment Black-7.

[0136] Amount of addition of the color material to be added to thephoto-curable ink is determined considering coloring property or soafter dispersion, where a preferable range is 0.1 to 15 wt %. The amountof addition of the color material less than 0.1 wt % raises a problem ofinsufficient coloring by the color material, and of degraded colorreproducibility of images produced on the recording medium P. The amountof addition of the color material exceeding 15 wt % raises problems ofdelayed curing of the ink dots under UV irradiation, and of degradedimage quality due to bleeding of the ink dots.

[0137] The pigment can be dispersed into the photo-curable ink using aball mill, sand mill, attriter, roll mill, agitator, Henshel mixer,colloid mill, ultrasonic homogenizer, pearl mill, wet jet mill, paintshaker or the like.

[0138] It is also possible to add a dispersion aid to the photo-curableink, in order to disperse the pigment in the photo-curable ink. Polymerdispersion aid is preferably used as the dispersion aid. SolsperseSeries produced by Avecia KK is typically used as the polymer dispersionaid. It is also allowable to add a synergist as the dispersion auxiliaryto the photo-curable ink corresponding to species of the pigments.

[0139] The dispersion aid and dispersion auxiliary are preferably addedin an amount of 1 to 50 weight parts per 100 weight parts of thepigment. The amount of addition of the dispersion aid and dispersionauxiliary per 100 weight parts of the pigment of less than 1 weight partraises problems of non-uniform dispersion of the pigment in thephoto-curable ink, and of considerable degradation in image qualityproduced on the recording medium P. On the other hand, the amount ofaddition of the dispersion aid and dispersion auxiliary per 100 weightparts of the pigment exceeding 50 weight parts raises a problem ofinsufficient coloring of the color material or delayed curing of thephoto-curable ink after placed on the recording medium P.

[0140] Solvent or polymerizable composition is applied to a dispersionmedium for dispersing the pigment into the photo-curable ink. Herein, itis preferable to disperse the pigment in the photo-curable ink only bythe polymerizable composition in order to cure the photo-curable inkapplicable to the present invention rapidly under UV irradiation and toprevent deterioration or odor of the photo-curable ink after the curing.It is also preferable to apply a monomer having a low viscosity for thepolymerizable composition in order to disperse the pigment in thephoto-curable ink without using any solvent.

[0141] In the dispersion of the pigment, average grain size of thepigment is preferably controlled within a range from 0.08 to 0.5 μm. Thegrain size of the pigment is measured by the light scattering method,and the average grain size is defined by histogram average (D₅₀). Theaverage grain size of pigment less than 0.08 μm raises a problem ofincrease in the costs for the photo-curable ink. The average grain sizeof pigment exceeding 0.5 μm raises a problem of ruining of transparencyof the photo-curable ink after placed on the recording medium P, ordegradation of image quality due to delayed curing of the photo-curableink under UV irradiation.

[0142] Maximum grain size of the pigment is preferably controlled withina range from 0.3 to 10 μm. The maximum grain size smaller than 0.3 μmraises a problem of increase in the costs for the photo-curable ink. Themaximum grain size larger than 10 μm raises a problem that thephoto-curable ink is more likely to clog in the nozzle. For thesereasons, the maximum grain size of the pigment is more preferablycontrolled within a range from 0.3 to 3 μm.

[0143] The components contained in the photo-curable ink are by no meanslimited to those described in the above. For example, it is allowable toadd a polymerization inhibitor in an amount of 200 to 20,000 ppm in thephoto-curable ink, in order to prevent the photo-curable ink from beingcured before ejected. In particular for the case where the photo-curableink is prepared as having a high viscosity, and ejected under heating soas to lower the viscosity, it is preferable to add the polymerizationinhibitor to the photo-curable ink in order to avoid clogging in thehead due to thermal polymerization.

[0144] Besides the components described in the above, it is alsoallowable to optionally add surfactant; leveling additive; mattingagent; and polyester-base resins, polyurethane-base resins, vinyl-baseresins, acrylic resins, rubber-base resins and waxes for controlling thefilm properties, in the photo-curable ink. It is also effective to add atrace amount of organic solvent in the photo-curable ink, in order toimprove contact adhesiveness between the recording medium P and thephoto-curable ink. In this case, the addition is effective only within arange not causative of problems of solvent resistance or odor, where theamount of addition preferably falls within a range from 0.1 to 5 wt %,and more preferably from 0.1 to 3 wt %.

[0145] It is still also allowable to blend the photo-curable ink byusing a long-life initiator and a cation-polymerizable monomer incombination, or to blend a hybrid-type, photo-curable ink by using aradical-polymerizable composition and a cation-polymerizable compositionin combination, as a means for preventing lowering of the sensitivity ofink color materials due to shielding effect.

[0146] The method for forming the image on the recording medium P byusing the ink-jet printer 1 according to the present invention will beexplained, as follows.

[0147] The image is printed by ejecting the photo-curable ink to therecording medium P from the ink-jet heads 2, 2 and so on. At the time,when the ink-jet heads 2, 2 and so on are moved in the left directionshown in FIG. 2B on the recording medium P, by the carriage 21, thephoto-curable ink is ejected to the recording medium P. When thephoto-curable ink ejected from the ink-jet heads 2, 2 and so on, areplaced on the recording medium P in order, the ink dots are formed. Theink dots are expanded on the recording medium P by leveling.

[0148] When ink-jet heads 2, 2 and so on eject the photo-curable inktherefrom, the light emitting section 231 emits and irradiates UVradiation to the ink dots. When the ink-jet heads 2, 2 and so on formsthe ink dots, the carriage 21 moves so that the light irradiationsection 23 is located above the ink dots. After the carriage 21 moves,when the galvanometer mirror 232 a operates and deflects the opticalpath of the UV radiation, the ink dots are scanned with the UVradiation.

[0149] Herein, as described above, the timing and the period thegalvanometer mirror 232 a deflects UV radiation are determined within arange from 0.02 to 500 ms after the ink dots are formed so that the inkdots are expanded to the proper dot diameter by leveling, and cured.Further, the length in the “S” direction of the range of UV radiationirradiated when scanned by the galvanometer mirror 232 a one time isdetermined so as to be substantially equal to the length in the “S”direction of the range to which the ink dots are formed when the ink isejected from the ink-jet head 2 one time. Further, the luminance of theUV radiation irradiated from the light irradiation section 23 isdetermined to be 1000 mW/cm² or higher, so that the ink dots are curedrapidly.

[0150] The ejection of the photo-curable ink and the irradiation of UVradiation are done when the carriage 21 moves in the left directionshown in FIG. 2B. When the carriage 21 moves from the right end to theleft end of the recording medium P, one step of printing images is done.Thereafter, when the recording medium P is carried by a proper distancein the “S” direction by the relative moving section, the carriage 21returns to the right end of the recording medium P. Thereby, the nextstep of printing images is done. When the steps are done continuously,the desired images are printed on the recording medium P.

[0151] The example of the ink-jet printer 1 according to theabove-described embodiment, will be explained, as follows.

[0152] In this example, a magenta ink MI1 and a cyan ink CI1 areprepared as described below, and are applied as the photo-curable inks.In the preparation of the photo-curable inks, pigments, dispersion aidsand so forth are first blended according to the compositions below, andthe mixtures are then kneaded and dispersed using a two-roll mill, tothereby obtain magenta pigment dispersion MP1 and cyan pigmentdispersion CP1. <Magenta pigment dispersion MP1> Pigment Violet 19(pigment) 70 weight parts nonionic dispersion aid (dispersion aid) 10weight parts phenoxypolyethylene glycol acrylate 20 weight parts(polymerizable composition) Sumilizer GS (polymerization inhibitor, 0.1weight parts  product of Sumitomo Chemical Co., Ltd.) <Cyan pigmentdispersion CP1> Pigment Blue 15:3 (pigment) 70 weight parts nonionicdispersion aid (dispersion aid) 10 weight parts phenoxypolyethyleneglycol acrylate 20 weight parts (polymerizable composition) Sumilizer GS(polymerization inhibitor, 0.1 weight parts  product of SumitomoChemical Co., Ltd.)

[0153] Using the above-described pigment dispersions MP1 and CP1, theindividual photo-curable inks having specific colors are prepared byblending as shown in Table 1. In the blending of the photo-curable inks,all materials shown in Table 1, but excluding the pigment dispersion,are blended, and after a thorough dissolution is confirmed, the mixtureis gradually added with the aforementioned pigment dispersion at 50° C.,and the mixture is thoroughly stirred using a dissolver. Thus-blendedmaterial is pre-filtered through a 10-μm filter, and then filteredthrough a 0.8-μm filter to thereby remove particularly coarse grains.TABLE 1 MP1 CP1 DPCA60 TEGDA PO-A I907 DETX Magenta 4 25 25 44 1.5 0.5Ink MI1 Cyan 3 25 25 45 1.5 0.5 Ink CI1

[0154] The abbreviations in Table 1 denote the following materials:

[0155] DPCA60: KAYARAD DPCA, product of Nippon Kayaku Co., Ltd.

[0156] (caprolactam-modified dipentaerythritol hexaacrylate)

[0157] TEGDA: bis-Coat#335HP, product Osaka Organic Chemical Industry,Ltd.

[0158] (tetraethylene glycol diacrylate)

[0159] PO-A: light acrylate PO-A, product of Kyoeisha Chemical Co., Ltd.

[0160] (phenoxyethyl acrylate)

[0161] I907: initiator, Irgacure907, product of CIBA SpecialtyChemicals, K.K.

[0162] (2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropane-1-one)

[0163] DETX: initiation auxiliary, diethylthioxanthone

[0164] In the aforementioned filtering process, a sufficient filtrationspeed is obtained without causing any pressure loss. Next,thus-filtered, photo-curable ink is placed in a reduced pressure underheating and stirring at 50° C. in order to remove any dissolved air andwater, and the resultant ink is subjected to image printing.Thus-prepared, photo-curable ink is found to have a viscosity at 25° C.of 12 to 22 mPa.s, a surface tension of 24 to 30 mN/m, an average grainsize of pigment of 0.08 to 0.3 μm, and a water content of 0.7 to 1.2%.

[0165] The images are printed on the recording medium P, by using thephoto-curable ink prepared as described above. A polyethyleneterephthalate film is applied to the recording medium P on which theimages are printed. The ink-jet head 2 applied to the ink-jet printer 1used for printing images has 256 nozzles arranged on a line at a nozzlepitch of 360 dpi. Each nozzle has a diameter of 23 μm, and thephoto-curable ink of 8 pl is ejected from each nozzle. The carriage 21having the ink-jet heads 2, 2 and so on scans recording medium P in theA direction at 0.8 m/s.

[0166] A high-output pulse UV laser having an oscillating wavelength of355 nm is applied to the light emitting section 231 of the lightirradiation section 23. The beam diameter of the laser beam emitted asUV radiation from the light emitting section 231 is 3.5 mm, and theinstantaneous luminance of the laser beam is 30 W/cm² at the exposure ofthe pulse light (the average luminance is 24 mW/cm²)

[0167] The galvanometer mirror 232 a is provided at a position apartfrom the nozzle of the ink-jet head 2 rightward in the A direction shownin FIG. 2A, by 16 mm. Further, the timing or the period of operating thegalvanometer mirror 232 a is determined so that the laser beam isirradiated to the range to which the ink dots are formed after 20 mssince the photo-curable ink is placed on the recording medium P, and therange is scanned by the laser beam for 7 ms.

[0168] The image is printed on the recording medium P by carrying thecarriage 21 in the “A” direction and carrying the recording medium P bythe shorter distance than the nozzle pitch, four times, continuously,for every range, so as to form the image having the dot density of 720dpi on the recording medium P.

[0169] The images are printed on the recording medium P, by performingthe ejection of the magenta ink MI1 and the cyan ink CI1 from theink-jet heads 2, 2 and so on, and the scanning with the laser beam,continuously. As a result, it is confirmed that the ink dots on therecording medium P are cured without bleeding. The reason is that thehigh concentrated reactive species are generated by the initiator addedin the magenta ink MI1 and the cyan ink CI1, and the polymerizablecomposition is changed to the polymer compound rapidly before inhibitedby oxygen in the air, by irradiating the UV radiation having highluminance of 30 W/cm² to the ink dots.

[0170] According to the above-described example, it is possible toconfirm that the ink-jet printer 1 according to the first embodiment,can reduce the bleeding of the photo-curable ink effectively, and formhigh-quality images on the recording medium P.

[0171] As described above, when the UV radiation is rapidly irradiatedto the range on which the ink dots are formed by ejecting the ink fromthe ink-jet heads 2, 2 and so on, one time, it is possible to preventthe ink dots from bleeding on the recording medium. The above-describedUV radiation is emitted from the light emitting section 231 having adevice such as a laser or a LED, and irradiated to the above-describedink dots by scanning. Because the UV radiation emitted from the deviceis condensed and changed to the parallel rays easily, it is possible toirradiate the UV radiation to the ink dots on the recording medium P aslaser beam having high luminance. Therefore, it is possible to cure theink dots rapidly. Accordingly, when the ink is exposed properly by thelaser beam, it is possible to expose the ink at the extremely highluminance. As a result, it is possible to reduce the amount of additionof the expensive initiator, and reduce the cost of the ink.

[0172] Further, it is possible to easily prepare the compact and lightscanning section 232 for scanning with UV radiation emitted from thelight emitting section 231. Therefore, if the composition elements aremounted on the carriage 21, it is possible to prevent the carriage frombulking or begin heavier. Accordingly, it is possible to easily realizeboth the rapid irradiation of UV radiation to the ink dots and thescanning of the ink dots by the carriage 21 effectively. As a result, itis possible to prepare the ink-jet printer 1 which can printhigh-quality images without the bleeding of the photo-curable ink,effectively. Further, it is possible to prepare the compact ink-jetprinter 1 as described above.

[0173] Further, because the energy radiation emitted from the lightemitting section 231 is UV radiation having a wavelength of 250 nm orlonger, it is possible to apply a well-known device which can be goteasily, to the light emitting section 231. Accordingly, it is possibleto prepare the ink-jet printer 1 easily, at low cost. In addition,because the photo-curable ink corresponding to UV radiation having awavelength of 250 nm or longer, can be made of well-known materialswhich can be got easily, it is possible to prepare the ink applied tothe ink-jet printer 1 at low cost.

[0174] Further, because the direction in which the scanning section 232scans the ink dots by UV radiation is substantially parallel to thedirection in which the nozzles are arranged, it is possible to reducethe difference of time between ink dots, the time after each ink dot isformed on the recording medium P until it is irradiated with UVradiation, and to control the diameter or the shape of the ink dotuniformly. As a result, it is possible to print high-quality images onthe printing medium P.

[0175] The ink-jet printer 1 according to the embodiment is not limitedto the above-described one. The light irradiation section 23 may beprovided apart from the carriage 21.

[0176] For example, one light emitting section 231 may be provided at aposition apart from the carriage 21, as shown in FIG. 5A, and irradiateUV radiation to each galvanometer mirror 232 a. In case the lightemitting section 23 s has a bulky structure like a gas laser oscillator,when the light emitting section 23 s may be provided as shown in FIG.5B, it is possible to lighten the carriage 21.

[0177] [Second Embodiment]

[0178] Next, the ink-jet printer 1 according to the second embodimentwill be explained as follows. In the following explanation, it isomitted to explain the common section to one of the ink-jet printer 1according to the first embodiment, in detail.

[0179] The ink-jet printer 1 according to the second embodiment, printsthe images according to an external surface drum scanning system. Theink-jet printer 1 comprises the printing section 20, the lightirradiation section 23, a relative moving section 70 and so on.

[0180] The printing section 20 comprises the ink-jet head 2, thecarriage 21 and so on. The carriage 21 moves in the direction of thearrow “A” shown in FIGS. 3A and 3B with holding the ink-jet heads 2, 2and so on, and the scanning section 232 of the light irradiation section23, and scans on the recording medium P.

[0181] A plurality of ink-jet heads 2, 2 and so on are arranged in the“A” direction shown in FIG. 3A, so as to correspond to colors (Herein,yellow, magenta, cyan) of ink ejected to the recording medium P.

[0182] A plurality of nozzles for ejecting the photo-curable ink andforming the ink dots on the recording medium P are provided on thenozzle surface 2 a which is a surface to the recording medium P. Thenozzles are arranged in a condition that they can form a substantiallyparallel line to the direction of the arrow “A” shown in FIG. 3A, whencontained in the carriage 21, and they can form the ink dots on therecording medium P when ejecting photo-curable ink of the length “1”shown in FIG. 3A one time. Preferably, the distance between the nozzlesarranged is determined so as to form the ink dots having the density of300 dpi (dots per inch) or higher on the recording medium P, by ejectingthe ink one time, in order to form clear images on the recording mediumP effectively.

[0183] The light irradiation section (energy radiation irradiationsection) 23 comprises the light emitting section 231, the scanningsection 232, the collimator (which is not shown in figures) and so on.Further, the light irradiation section 23 is provided near the ink-jetheads 2, 2 and so on, in the vertical direction to the “A” direction.When the light irradiation section 23 scans the range of the recordingmedium P, on which the ink dots are formed, with the UV radiation, theink dots are cured.

[0184] The light emitting section 231 and the collimator are arranged ata position apart from the carriage 21. The light emitting section 231comprises a well-known light emitting device which is a laser elementsuch as a LED, a semiconductor laser element or the like. Preferably,the wavelength of UV radiation emitted from the light emitting section231 is within a range from 250 to 450 nm. Preferably, the collimator isdetermined so as to condense the UV radiation and change it to theparallel rays so that the luminance of the energy of the UV radiationemitted from the light emitting section 231 is 1000 mW/M² or higher whenthe UV radiation reaches the recording medium P.

[0185] The scanning section 232 functions also as the irradiationcontrol section. The scanning section 232 comprises the galvanometermirror 232 a and a motor which is not shown in figures. The galvanometermirror 232 a periodically changes the angle against the light emittingsection 231 by the motor. Thereby, the galvanometer mirror 232 adeflects the optical path of the UV radiation emitted from the lightemitting section 231 periodically, and scans on the recording medium P.

[0186] The length (the length in the “A” direction shown in FIG. 3A) ofthe range on the recording medium P to which the UV radiation isirradiated from the light irradiation section 23, is determined so as tobe substantially equal to “1” which is the length in the “A” direction,of the range on the recording medium P on which the ink dots are formedwhen the ink is ejected from the ink-jet heads 2, 2 and so on one time.Because the length of the above-described range is determined asdescribed above, it is possible to irradiate the UV radiation so as tocorrespond to the recording width of the ink-jet heads 2, 2 and so on.

[0187] The period and the timing of the deflection of the UV radiationby the galvanometer mirror 232 a is determined properly in considerationof the dot diameter required for the ink dot, the moving speed of thecarriage 21, the property of the photo-curable ink or the like, so thatthe time after the photo-curable ink ejected from the ink-jet head 2 isplaced on the recording medium P until it is irradiated with the UVradiation is within a range from 0.02 to 500 ms.

[0188] The relative moving section 70 comprises a drum 71, a drivingrotating section (which is not shown in figures) and so on. The drum 71is formed in a cylindrical shape. The recording medium P is attached onan external surface of the drum 71. The driving rotating section rotatesthe drum 71 in the direction (S direction) of the arrow “S” show in FIG.3A. Thereby, the recording medium P relatively moves to the ink-jetheads 2, 2 and so on.

[0189] Preferably, the speed that the driving rotating section rotatesthe drum 71 is determined so that the speed that the recording medium Prelatively moves to the ink-jet heads 2, 2 and so on is within a rangefrom 0.3 to 200 m/s. The speed lower than 0.3 m/s causes a problem thatthe efficiency of printing the image on the recording medium P islowered. On the other hand, the speed higher than 200 m/s causes aproblem that it is required to prepare the large-size relative movingsection, and it is impossible to prepare the compact ink-jet printer 1.

[0190] The photo-curable ink substantially common to one explained inthe first embodiment is applied to the above-described ink-jet printer1.

[0191] The method for printing images by the ink-jet printer 1 accordingto the second embodiment will be explained as follows.

[0192] The images are printed by ejecting the photo-curable ink from theink-jet heads 2, 2 and so on to the recording medium P. When thephoto-curable ink ejected from the ink-jet heads 2, 2 and so on isplaced on the recording medium P in order, the ink dots are formed.

[0193] After the photo-curable ink is ejected from the ink-jet heads 2,2 and so on, the light emitting section 231 emits and irradiates the UVradiation to the ink. When the ink dots based on the ink ejected fromthe ink-jet heads 2, 2 and so on are formed, the driving rotatingsection rotates in the “S” direction so that the light irradiationsection 23 is located above the ink dots. When the recording medium P ismoved, the galvanometer mirror 232 a operates and deflects the opticalpath of the UV radiation. Thereby, the ink dots are scanned so that theUV radiation is irradiated after 0.02 to 500 ms since the photo-curableink is placed on the recording medium P. Therefore, the ink dots formingthe images on the recording medium P are expanded properly (with theproper diameter) and cured.

[0194] Herein, the length in the “A” direction of the range to which theUV radiation is irradiated when the galvanometer mirror 232 a scans onetime, is determined so as to be substantial equal to the length in the“A” direction of the range on which the ink dots are formed when the inkis ejected from the ink-jet heads 2, 2 and so one time. Further, theluminance of the UV radiation irradiated from the light irradiationsection 23 is determined to be 1000 mW/cm² or higher so that the inkdots are cured rapidly.

[0195] The scanning by the carriage 21 moving in the “A” direction andthe scanning by the drum rotating in the “S” direction are performedwhen the ink dots ejected from the ink-jet heads 2, 2 and so on areformed and the UV radiation is irradiated from the light irradiationsection 23. Because the scanning by the drum 71 rotating and thescanning by the carriage 21 moving are combined and performed properly,it is possible to scan the whole recording medium P and print thedesired images on the recording medium P.

[0196] As described above, in case the present invention is applied tothe ink-jet printer 1 according to the external surface drum scanningsystem, it is possible to prevent the ink dots formed on the recordingmedium from bleeding, control the dot diameter, and cure the ink dotsrapidly. Further, it is possible to cure the ink dots without loweringthe efficiency of the ejection of the photo-curable ink from the ink-jetheads 2, 2 and so on. Furthermore, it is possible to prepare the compactink-jet printer 1 as described above. Accordingly, it is possible toprepare the compact ink-jet printer 1 which can print high-qualityimages without the bleeding of the photo-curable ink, efficiently.

[0197] [Third Embodiment]

[0198] Next, the ink-jet printer 1 according to the third embodimentwill be explained as follows. The ink-jet printer 1 according to thethird embodiment prints images according to the line recording system.The ink-jet printer 1 comprises the printing section 20, the lightirradiation section 23, the relative moving section (which is not shownin figures) and so on.

[0199] The printing section 20 comprises the ink-jet head 2, thecarriage 21 and so on, as shown in FIGS. 4A and 4B. The carriage 21 isfixed on the recording medium P with holding the ink-jet heads 2, 2 andso on and the light irradiation section 23.

[0200] The ink-jet heads 2, 2 and so on are formed as a line head. Thatis, nozzles of the length “1” which is the substantially same as orlonger than one of the recording medium P in the A direction, areprovided on the nozzle surface 2 a of the ink-jet head 2. Further, thenozzles are arranged in a substantial parallel line to the “A”direction. When the nozzles are provided as described above, it ispossible to form the ink dots arranged at one row or a plurality rows ofthe length “1” in the “A” direction of the recording medium P, at thesubstantially same time, without moving the carriage 21.

[0201] A plurality of ink-jet heads 2, 2 and so on are arranged, fixedand provided in the “S” direction shown in FIG. 4B, so as to correspondto colors (Herein, yellow, magenta, cyan, black) of the ink ejected tothe recording medium P.

[0202] Preferably, the distance between the nozzles provided isdetermined so as to form the ink dots having the density of 300 dpi(dots per inch) or higher on the recording medium P by ejecting the inkone time, in order to form clear images on the recording medium Pefficiently. The reason is that the light is not always exposed to onlythe range on which the ink is placed, according to the laser beamirradiation method applied to the present invention. For example, whenthe nozzle pitch is 150 dpi, in order to obtain the image having 600dpi, it is necessary to scan at least four times. In the case, theefficiency of the light irradiation is ¼. When the nozzle pitch is 300dpi, the efficiency is ½. Therefore, the nozzle pitch of 300 dpi is moreefficient than the nozzle pitch 150 dpi. In order to obtain high fineimages light-irradiation-efficiently, it is preferable to use the headhaving the nozzle pitch of 300 dpi or higher.

[0203] The light irradiation section (energy radiation irradiationsection) 23 comprises the light emitting section 231, the scanningsection 232, the collimator (which is not shown in figures) and so on.The light irradiation sections 23, 23 and so on and the ink-jet heads 2,2 and so on are arranged and fixed by turns, in the “S” direction asshown in FIG. 4B. The light irradiation section 23 irradiates the UVradiation to the range on which the ink dots are formed, and cures theink dots.

[0204] The light emitting section 231 comprises a well-known lightemitting device which is a laser element such as a LED, a semiconductorlaser element or the like. Preferably, the wave length of the UVradiation emitted from the light emitting section 231 is within a rangefrom 250 to 450 nm. Further, preferably, the collimator is determined soas to condense the UV radiation emitter from the light emitting section231 and change it to parallel rays, so that luminance of the UVradiation is 1000 mW/m² or higher when the UV radiation reaches therecording medium P.

[0205] The scanning section 232 function also as the irradiation controlsection. The scanning section 232 comprises the galvanometer mirror 232a and a motor which is not shown in figures. The galvanometer mirror 232a changes the angle against the light emitting section 231 by the motor,periodically, and changes the optical path of the UV radiation emittedfrom the light emitting section 231. Thereby, the range on the recordingmedium P is scanned by the UV radiation.

[0206] The length (the length in the “A” direction shown in FIG. 4A) ofthe range on the recording medium P, to which the UV radiation isirradiated from the light emitting section 23 is determined so as to bethe substantially same as the length “1” of the range in the “A”direction on the recording medium P on which the ink dots are formedwhen the ink-jet heads 2, 2 and so on eject ink one time. Therefore, therange on the recording medium P to which the UV radiation is irradiatedis determined so as to correspond to the recording width of the ink-jetheads 2.

[0207] The period and the timing of the deflection of the UV radiationby the galvanometer mirror 232 a is determined properly in considerationof the dot diameter required for the ink dot, the moving speed of thecarriage 21, the property of the photo-curable ink or the like, so thatthe time after the photo-curable ink ejected from the ink-jet heads 2 isplaced on the recording medium P until it is irradiated with the UVradiation is within a range from 0.02 to 500 ms.

[0208] The relative moving section carries the recording medium P in the“S” direction vertical to the “A” direction which is the direction ofthe nozzles arranged in the ink-jet heads 2, 2 and so on which is a linehead. Thereby, the relative moving section moves the recording medium Pto the ink-jet heads 2, 2 and so relatively. Preferably, the carryingspeed of the recording medium P is determined to be within a range from0.3 to 5 m/s. The speed lower than 0.3 m/s causes a problem that theefficiency of printing the images on the recording medium P is lowered.On the other hand, the speed higher than 5 m/s causes a problem that itis required to prepare the large-sized relative moving section, and itis impossible to prepare the compact ink-jet printer 1.

[0209] The photo-curable ink substantially common to one explained inthe first embodiment is applied to the above-described ink-jet printer1.

[0210] Next, the method for printing images by the ink-jet printer 1according to the third embodiment will be explained as follows.

[0211] The images are printed by ejecting the photo-curable ink from theink-jet heads 2, 2 and so on to the recording medium P. Thephoto-curable ink ejected from the ink-jet heads 2, 2 and so on isplaced on the recording medium P, in order. Therefore, one row of inkdots are formed in the “A” direction of the range on the recordingmedium P on which the images can be printed.

[0212] When the photo-curable ink is ejected from the ink-jet heads 2, 2and so on, it is irradiated with the UV radiation irradiated from thelight emitting sections 231, 231 and so on. When the ink dots ejectedfrom the ink-jet heads 2, 2 and so are formed, the driving rotatingsection drives in the “S” direction so as to locate the lightirradiation section 23 above the ink dots.

[0213] When the galvanometer mirror 232 a operates and deflects theoptical path of the UV radiation with moving the recording medium P, theUV radiation is irradiated to the ink after 0.02 to 500 ms since thephoto-curable ink is placed on the recording medium P. Therefore, theink dots are scanned. Accordingly, the ink dots forming images on therecording medium P are expanded properly (with a proper dot diameter),and cured.

[0214] Herein, the length in the “A” direction of the range to which thegalvanometer mirror 232 a is scanned with the UV radiation one time, isdetermined so as to be the substantially same as the length “1” in the“A” direction of the range on which the ink dots are formed when the inkis ejected from the ink-jet heads 2, 2 and so on one time. Further, theluminance of the UV radiation irradiated from the light irradiationsection 23 is determined to be 1000 mW/cm² or higher so that the inkdots are cured rapidly.

[0215] Even when the ink dots ejected from the ink-jet heads 2, 2 and soare formed and irradiated with the UV radiation emitted from the lightirradiation section 23, the carriage 21 moves in the “S” direction by aproper distance. Thereby, the scanning is performed in the “S”direction. Therefore, when performing the scanning continuously, it ispossible to print the desired images on the recording medium P.

[0216] Next, an example of printing images on the recording medium P bythe ink-jet printer 1 according to the embodiment will be explained asfollows.

[0217] In this example, magenta ink MI2 and cyan ink CI2 are prepared asdescribed below, and are applied as the photo-curable inks. In thepreparation of the photo-curable inks, pigments, dispersion aids and soforth are first blended according to the compositions below, and themixtures are then kneaded and dispersed using a two-roll mill, tothereby obtain magenta pigment dispersion MP2 and cyan pigmentdispersion CP2. <Magenta pigment dispersion M2> Pigment Violet 19(pigment) 70 weight parts nonionic dispersion aid (dispersion aid) 10weight parts di [1-ethyl-(3-oxetanyl)]methyl ether 20 weight parts(polymerizable composition; OXT-221, product of Toagosei Co., Ltd.)<Cyan pigment dispersion C2> Pigment Blue 15:3 (pigment) 70 weight partsnonionic dispersion aid (dispersion aid) 10 weight parts di[1-ethyl-(3-oxetanyl)]methyl ether 20 weight parts (polymerizablecomposition; OXT-221, product of Toagosei Co., Ltd.)

[0218] Using thus-prepared pigment dispersions, the individualphoto-curable inks having specific colors are prepared by blending asshown in Table 2 similarly to as described in the example of the firstembodiment. Thus-prepared, photo-curable inks are found to have aviscosity at 25° C. of 15 to 30 mPa.s, a surface tension of 30 to 38mN/m, an average grain size of pigment of 0.08 to 0.2 μm, and a watercontent of 0.3 to 0.7%. TABLE 2 MP2 CP2 OXT-221 2021P SP152 AnthraceneMagenta 4 25 28.5 1.3 0.2 Ink MI2 Cyan 3 25 28.5 1.3 0.2 Ink CI2

[0219] The abbreviations in Table 2 denote the following materials:

[0220] OXT-221: polymerizable composition, OXT-221, product of ToagoseiCo., Ltd.

[0221] (di[1-ethyl-(3-oxetanyl)]methyl ether)

[0222] 2021P: polymerizable composition, Celloxide 2021P, product ofDaicel Chemical Industries, Ltd.

[0223] (3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate)

[0224] SP152: initiator, SP152, product of Asahi Denka Co., Ltd.

[0225] (triphenylsulfonium-salt-based, photo-acid generator) anthracene:initiation auxiliary

[0226] The images are printed by using the photo-curable ink prepared asdescribed above, according to the line recording system. A polyethyleneterephthalate film is applied to the recording medium P.

[0227] The ink-jet head 2 applied to the ink-jet printer 1 has 256nozzles arranged on a line at a nozzle pitch of 360 dpi. Each nozzle hasa diameter of 23 μm, and the photo-curable ink of 28 pl is ejected fromeach nozzle when a piezo element operates.

[0228] A UV laser (continuous wave oscillation type) having anoscillating wavelength of 266 nm is applied to the light emittingsection 231. The collimator is determined so that the diameter of thelaser beam is 3.5 mm, and the luminance of the laser beam is 3 W/cm².

[0229] The laser beam emitted from the light emitting section 231, as UVradiation is irradiated on the recording medium P in the “A” directionshown in FIG. 4A, by the galvanometer mirror 232 a. The galvanometermirror 232 a is provided at a distance of 600 mm in the “A” directionfrom the corresponding ink-jet head 2 which is provided at the rightside in FIG. 4B. The timing and the period of the deflection of thelaser beam by the galvanometer mirror 232 a is determined so that thelaser beam is irradiated to the range on which the ink dots are formed,for 1.75 ms, after 30 ms since the ink dots are formed on the recordingmedium P. The carrying speed of the recording medium P by the relativemoving section is determined to be 2 m/s.

[0230] The images are printed on the recording medium P by performingthe ejection of the magenta ink MI2 and the cyan ink CI2 from theink-jet heads 2, 2 and so on, and the scanning with the laser beam,continuously, in the above-described condition. As a result, it isconfirmed that the ink dots on the recording medium P are cured withoutbleeding. That is, the magenta ink MI2 and the cyan ink CI2 are curedrapidly for the same reasons as those according to the first embodiment.

[0231] According to the above-described example, it is confirmed thatthe ink-jet printer 1 according to the third embodiment can reduce thebleeding of the photo-curable ink effectively and can form high-qualityimages on the recording medium P.

[0232] As described above, in case of applying the present invention tothe ink-jet printer 1 of the line recording system, it is possible toprevent the ink dots formed on the recording medium P from bleeding, andcure the ink dots rapidly with controlling the dot diameter of the inkdots. Further, it is possible to cure the ink dots without lowering theefficiency of ejecting the photo-curable ink from the ink-jet heads 2, 2and so on. Further, it is possible to prepare the compact ink-jetprinter 1. Accordingly, it is possible to prepare the compact ink-jetprinter 1 which can print high-quality images without the bleeding ofthe photo-curable ink, efficiently.

[0233] The ink-jet printer 1 according to the embodiment, is not limitedto have the ink-jet heads 2, 2 and so on fixed thereto. The ink-jetheads 2, 2 and so on may be provided so as to move in a shorter distancethan the pitch of the nozzles. In the case, when the carriage 21 movesin a distance which is ½ or ⅓ of the nozzle pitch, it is possible toprint high-quality images having a high resolution.

[0234] The ink-jet printer 1 according to the embodiment may have acombination structure of the line head recording system and the externalsurface drum scanning system. That is, as shown in FIG. 6, the recordingwidth of the ink-jet head 2 may be the substantially same as the width(in the “A” direction shown in FIG. 5) of the range of the recordingmedium P on which images can be printed. Further, the relative movingsection 70 may be provided at the drum 71, and the recording medium Pmay be attached on the external surface of the drum 71.

[0235] The image recording method and apparatus of the present inventionare not limited to the above-described method and apparatus.

[0236] The energy radiation irradiated to the ink dots by scanning isnot limited to UV radiation having a wavelength of 250 nm or longer.

[0237] For example, the image recording method and apparatus of thepresent invention may use energy radiation such as UV radiation, visibleradiation, infrared radiation, electron beam, X rays or the like, havinga wavelength shorter than 250 nm, and cure ink dots.

[0238] For example, it is allowable to use infrared radiation having awavelength of 800 nm or longer as the energy radiation in the imagerecording method and apparatus of the present invention. In this case,it is possible to apply an energy radiation curable ink having aproperty to be cured based on a thermal reaction. Applicable examples ofthe energy radiation curable ink include those using, as a thermalreaction initiator, peroxide compounds such as benzoyl peroxide, diazocompounds (heat radical generator) such as AIBN, and compounds in commonwith those the photo-acid generator exemplified in the first example. Itis also allowable to use an initiation auxiliary which strongly tend toradiate heat after absorbing near-infrared radiation, such as cyaninedye, squarylium dye, polymethine dye, carbon black and titanium black.As described above, in case infrared radiation having a wavelength of800 nm or longer is applied as the energy radiation, it is possible toapply a well-known device which can be got easily to the light emittingsection 231, and to prepare the energy radiation curable ink ofwell-known materials which can be got easily.

[0239] Further, it is allowable to use visible radiation having awavelength of 450 nm or shorter as the energy radiation. Thephoto-curable ink corresponding to the visible radiation causes aproblem that the initiator or the initiation auxiliary emits coloringand inhibits the color tone of the photo-curable ink. However, in thephoto-curable ink having a strong color tone like black, the coloring isnot affected. Therefore, in the ink-jet printer 1 for printing black andwhite images, it is possible to apply the radiation having a wavelengthof 450 nm or shorter as the energy radiation. In the case, it ispossible to apply a well-known device which can be got easily to thelight emitting section 231, and to prepare the energy radiation curableink of well-known materials which can be got easily.

[0240] The embodiment of the image recording apparatus of the presentinvention is not limited to the ink-jet printer 1 described in eachembodiment.

[0241] For example, the light emitting section 231 which is one ofelements of the light irradiation section 23 may be provided in theinside of the carriage 21, or may be provided apart from the carriage21.

[0242] Further, the scanning section 232 and the irradiation controlsection are not limited to the structure comprising the galvanometermirror 232 a, and may deflect the energy radiation by a polygon mirror.Further, the scanning section 232 and the irradiation control sectionmay apply an optical element as the lens or the like. Furthermore, thescanning section 232 and the irradiation control section may beseparated from each other.

[0243] Further, one light emitting section 231 may be provided for oneink-jet printer, and may irradiate energy radiation to a plurality ofscanning sections 232, 232 and so on. As described above, the specificcondition of the light irradiation section 23 is determined based on thedesign, properly, in consideration of not only the efficiency regardingthe ink dot curing, but also the efficiency of the whole image printing,the shape of the ink-jet printer 1 or the like.

[0244] According to the present invention, because energy radiation isirradiated to ink dots formed on the recording medium rapidly, it ispossible to prevent the ink from bleeding and print high-quality images.Further, because the effect can be obtained by the energy radiationirradiation section which is compact, it is possible to printhigh-quality images and to prepare the compact image printing apparatuswhich can print high-quality images.

[0245] The entire disclosure of Japanese Patent Application No. Tokugan2002-133991 filed on May 9, 2002 including specification, claims,drawings and summary are incorporated herein by reference in itsentirety.

What is claimed is:
 1. An image recording method for ejecting andplacing energy radiation curable ink which is cured when irradiated withenergy radiation according to an ink-jet recording method, irradiatingthe energy radiation on a recording medium on which ink dots are formed,and printing an image, the method comprising: ejecting the energyradiation curable ink to the recording medium from a plurality ofnozzles provided for an ink-jet head, moving the recording medium to theink-jet head relatively, and forming the image; and controlling a rangeto which the energy radiation is irradiated, so as to correspond to arecording width of the ink-jet head.
 2. The method of claim 1, whereinthe energy radiation is emitted from at least one of a laser device anda LED, and the irradiating the energy radiation is performed by scanningthe recording medium with the energy radiation.
 3. The method of claim2, wherein the nozzles are arranged in a line, and the scanning therecording medium with the energy radiation is performed in asubstantially parallel direction to a direction in which the nozzles arearranged.
 4. The method of claim 1, wherein the moving the recordingmedium to the ink-jet head relatively includes moving the recordingmedium to the ink-jet head relatively by rotating a cylindrical drumhaving an external surface on which the recording medium is attached. 5.The method of claim 1, wherein the ink-jet head is a line head, and themoving the recording medium to the ink-jet head relatively includesmoving the recording medium to the ink-jet head relatively by carryingthe recording medium in a vertical direction to the line head.
 6. Themethod of claim 1, wherein the nozzles are arranged so as to form theink dots having a density of 300 dpi or higher on the recording mediumwhen irradiating the energy radiation curable ink therefrom one time. 7.The method of claim 1, wherein a wavelength of the energy radiation iswithin a range from 250 to 450 nm or 800 nm or longer.
 8. The method ofclaim 1, wherein a luminance of the energy radiation irradiated to therecording medium is 1000 mW/cm² or higher.
 9. The method of claim 2,wherein a time after the energy radiation curable ink is placed on therecording medium until the ink dots are scanned and irradiated with theenergy radiation is within a range from 0.02 to 500 ms.
 10. The methodof claim 1, wherein a speed of moving the recording medium to theink-jet head relatively is within a range from 0.3 to 200 m/s. 11.Energy radiation curable ink used for the image recording method of anyone of claims 1 to 10, comprising: a polymerizable composition to form apolymer compound through polymerization reaction, an initiator forinitiating the polymerization reaction when irradiated with the energyradiation, and a color material for coloring the energy radiationcurable ink, wherein the initiator initiates the polymerization reactionwhen irradiated with the energy radiation having a wavelength which iswithin a range from 250 to 450 nm or 800 nm or longer.
 12. The ink ofclaim 11, wherein amount of addition of the initiator is within a rangefrom 0.1 to 3 wt %.
 13. The ink of claim 11, further comprising aninitiation auxiliary for giving excitation energy to the initiator whenirradiated with the energy radiation, and making the initiator initiatethe polymerization reaction.
 14. An image recording apparatus forejecting and placing energy radiation curable ink which is cured whenirradiated with energy radiation according to an ink-jet recordingmethod, irradiating the energy radiation on a recording medium on whichink dots are formed, and printing an image, the apparatus comprising: anink-jet head comprising a plurality of nozzles for ejecting the energyradiation curable ink, the ink-jet head for ejecting the energyradiation curable ink to the recording medium; a relative moving sectionfor moving the recording medium to the ink-jet head relatively; anenergy radiation irradiation section comprising a light emitting sectionfor emitting the energy radiation and an irradiation control section forcontrolling a range on the recording medium to which the energyradiation is irradiated, the energy radiation irradiation section forirradiating the energy radiation to a portion on the recording medium onwhich the ink dots are formed; wherein the apparatus prints the image onthe recording medium by ejecting the energy radiation curable ink to therecording medium from the ink-jet head, and moving the recording mediumto the ink-jet head relatively by the relative moving section, and theirradiation control section controls the range so as to correspond to arecording width of the ink-jet head.
 15. The apparatus of claim 14,wherein the energy radiation irradiation section comprises a scanningsection for scanning the recording medium by irradiating the energyradiation to the recording medium, the light emitting section emits theenergy radiation from at least one of a laser device and a LED, and theirradiation control section controls the range by controlling a portionof the recording medium scanned by the scanning section.
 16. Theapparatus of claim 15, wherein the nozzles are arranged in a line, andthe scanning section scans the recording medium with the energyradiation in a substantially parallel direction to a direction in whichthe nozzles are arranged.
 17. The apparatus of claim 14, wherein therelative moving section comprises a cylindrical drum having an externalsurface on which the recording medium can be attached, and a drivingrotating section for rotating the drum, and moves the recording mediumto the ink-jet head relatively by rotating the drum in a condition thatthe recording medium is attached on the external surface of the drum.18. The apparatus of claim 14, wherein the ink-jet head is a line head,and the relative moving section moves the recording medium to theink-jet head relatively by carrying the recording medium in a verticaldirection to the line head.
 19. The apparatus of claim 14, wherein thenozzles are arranged so as to form the ink dots having a density of 300dpi or higher on the recording medium when irradiating the energyradiation curable ink therefrom one time.
 20. The apparatus of claim 14,wherein a wavelength of the energy radiation emitted from the lightemitting section is within a range from 250 to 450 nm or 800 nm orlonger.
 21. The apparatus of claim 14, wherein the energy radiationirradiation section comprises a condenser for condensing the energyradiation, and the condenser condenses the energy radiation so that aluminance of the energy radiation irradiated to the recording medium is1000 mW/cm² or higher.
 22. The apparatus of claim 15, wherein thescanning section scans the recording medium with the energy radiation sothat the ink dots are irradiated with the energy radiation after 0.02 to500 ms since the energy radiation curable ink is placed on the recordingmedium.
 23. The apparatus of claim 14, wherein the relative movingsection changes a relative position of the recording medium to theink-jet head at a speed within a range from 0.3 to 200 m/s.